[Coco] [coco] video signal generation

[Gene Heskett]

On Friday 05 January 2007 12:45, jdaggett at gate.net wrote:
>Y ou may want to consider changing the electrolytic to ceramic if the
> value is not to high.  Albeit somewhat expensive, ceramic caps to about
> 10 uF are available.
>
I've not found them to be terribly dependable James.  Very low tolerance 
for any overvoltage.  The Panasonic dvc-pro's had a few of those here and 
there, and the failure rates were about 20% of the teeny little surface 
mount electrolytics around them.  So we carried them on the shelf too.  
Smallish qtys of course, but then we were buying the electrolytics on 100 
count tapes toward the last of my tenure in that chair.  The electrolytic 
failures were opens and high esr's, generally non-destructive, the 
ceramics crowbared, so we noticed the destruction quickly.  Things get 
interesting when you have to figure out which trace in a 6 layer board 
goes where so you can jumper the burnout.  I gave up and started 
replacing the whole board after a while, it was quicker.

I could say do it, but use ones rated at least 2x the supply voltage.  6 
volters on a 5 volt line don't cut it for the long haul.

>james
>
>On 4 Jan 2007 at 22:33, Gene Heskett wrote:
>> But, I just had another ugly thought.  The gime is a cmos chip, and as
>> such needs a seriously low impedance bypass capacitor right at its
>> supply pins to give its best performance vis a vis rise & fall times.
>> If that capacitor was say a 1 uf or thereabouts electrolytic, there is
>> no way in all creation that this capacitor is still good after what,
>> 19 to 20 years?
>>  The next time I have the top off mine, I WILL check that.  Anything
>>  more
>> than a few millivolts of noise there while its running should condemn
>> that capacitor to the out bin.  I'd be tempted to replace it with a
>> big low voltage paper or mylar of half a mic or so, which should last
>> at least till the rapture.  Electrolytics in that position (or any
>> similar such place in a circuit) are a ticking time bomb.

-- 
Cheers, Gene
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